Transforming Growth Factor-Beta Binds Reversibly in Vitro to Guglielmi Detachable Coils

Abstract

We determined the propensity for and reversibility of transforming growth factor-ß (TGFß) binding to uncoated Guglielmi Detachable Coils (GDC) and to GDC coated with extracellular matrix (ECM) proteins.

Three 1.0 centimetre samples each of uncoated GDC-18 and of GDC-18 coated with either poly-L-lysine, laminin, type I collagen, type IV collagen, fibronectin, or poly-L-lysine and laminin were prepared. These samples were immersed briefly in a solution containing I¹²⁵-labelled TGFß at a concentration of 0.225 μg/ml with initial specific activity of 123.3 mCi/mg (DuPont-NEN, Billerica, MA), and were counted using a scintillation counter. Each sample was then placed in a vial containing saline, shaken for 60 seconds, and counted again. Selected samples were immersed for varying periods within the TGFß solution and counted before and after saline rinse. Samples were rinsed one week after initial rinsing and counted again. The amount of binding between coil types was compared using the Student t test.

For all samples initial binding of TGFß was in the order of 60–120 pg/cm. For the pre-rinse data there were no statistically significant differences between the amount bound to any single coil coating type relative to other coatings. Compared to the initial accumulations, the amount remaining after rinsing ranged from 40% (poly-L-lysine) to 63% (poly-L-lysine with laminin), with a mean of 55% among the seven coil types. After rinsing there was more growth factor remaining on uncoated coils than on poly-L-lysine-coated coils (p=0.05), fibronectin-coated coils (p=0.01), and type IV collagen-coated coils (p=0.04). There was a trend toward greater residual growth factor on coils coated with poly-L-lysine and laminin compared to coils coated with poly-L-lysine alone (p=0.10). Delayed, second rinsing of the samples one week after initial testing demonstrated only minor incremental loss of TGFß from the coil surfaces. After five minutes of immersion, accumulation was approximately 200% greater than that noted with brief submersion, but immersions lasting over five minutes did not yield increasing levels of TGFß binding.

TGFß binds to GDC coils. Binding is not improved with ECM protein-coated coils compared to uncoated coils. The absolute amount of TGFß bound to the coil will likely result in local concentrations of growth factor in the order of those required for biological activity in vivo.